With the diminishing supply of crude mineral oil and fossil fuels in general, use of renewable energy sources is becoming increasingly important for the production of liquid fuels. These fuels from renewable energy sources are often referred to as biofuels.
Biofuels derived from non-edible renewable energy sources, such as cellulosic materials, are preferred as these do not compete with food production. These biofuels are also referred to as second generation biofuels or advanced biofuels. Most of these non-edible renewable energy sources, however, are solid biomass materials that are somewhat cumbersome to convert into liquid fuels.
One process that can be used for converting solid biomass into liquid fuels or other useful chemicals is fluid catalytic cracking (FCC), which has been widely used for some decades in fossil fuel refining.
Fluid catalytic cracking comprises mixing hot regenerated catalyst with a hydrocarbon feedstock in a riser reactor under catalytic cracking reaction conditions. This causes the feedstock to be cracked to yield hydrocarbon vapours (including for example gasoline-range boiling hydrocarbons, diesel-range boiling hydrocarbons, dry gas, liquefied petroleum gas and other hydrocarbons) as well as degradation products, for example coke, which deposit on the catalyst causing a reduction in catalytic activity. Hydrocarbon vapours and coked catalyst are passed from the top of the riser reactor to a separator vessel where catalyst is separated from hydrocarbon vapours. The separated catalyst is then passed to a stripper where it is contacted with a stripping gas to remove volatile product hydrocarbons. The stripped catalyst is then passed to a separate regeneration vessel where coke is oxidised from the catalyst. Catalyst having had a substantial portion of the coke removed is then passed to a regenerated catalyst standpipe to the riser reactor for cyclic reuse in the process.
Of particular concern in the field of fluid catalytic cracking has been the development of methods and systems for separating hydrocarbon vapours from catalyst particles under efficient separating conditions so as to reduce overcracking and improve product purity. Patent publications EP-A-162978, EP-A-629679, U.S. Pat. No. 5,248,411 and EP-A-604026 all describe developments concerned with the rapid separation and recovery of entrained catalyst particles from hydrocarbon vapour. The rapid separation is achieved in that the catalyst is separated from the reactor riser effluent in a first cyclone separator in fluid connection with a second cyclone. This cyclone line-up in fluid catalytic cracking reactors is also referred to as close-coupled cyclone separation provided that the primary and secondary cyclones are contained in one larger vessel.
More recently, fluid catalytic cracking has been proposed to process biomass, especially solid biomass. WO2010/135734 describes a method for co-processing a biomass feedstock and a refinery feedstock in a refinery unit comprising catalytically cracking the biomass feedstock and the refinery feedstock in a refinery unit comprising a fluidized reactor, wherein hydrogen is transferred from the refinery feedstock to carbon and oxygen of the biomass feedstock. In one of the embodiments in WO2010/135734, the biomass feedstock comprises a plurality of solid biomass particles having an average size between 50 and 1000 microns. In passing, it is further mentioned that solid biomass particles can be pre-processed to increase brittleness, susceptibility to catalytic conversion (e.g. by roasting, toasting, and/or torrefication) and/or susceptibility to mixing with a petrochemical feedstock.
A drawback of many prior art fluid catalytic cracking processes for converting biomass is that they are often based on equipment and/or principles of fluid catalytic cracking processes originally designed for fossil fuel feedstocks, particularly refinery feedstocks. This can lead to processes that are prone to providing impure products and/or require more frequent maintenance or component replacement.
It is an object of the invention to provide a method and/or apparatus that address at least one problem associated with the prior art.